RFID tags are known in the art. RFID tags are typically small circuits that are configured to respond to a radio-frequency (RF) signal with a corresponding data transmission. A device configured to transmit such an RF signal and to receive that responsive data transmission is often referred to as a reader. Some RFID tags are self-powered while others are passive in that they rely upon the received RF signal for their operating power (and some RFID tags are a hybrid of these two approaches).
Many times the RFID tag's data includes information, such as an identifier, that is unique (at least to some extent) to that particular responding RFID tag. The Electronic Product Code (EPC) as managed by EPCGlobal, Inc., for example, represents one such effort in these regards. EPC-based RFID tags each have an utterly-unique serial number (within the EPC system) to thereby uniquely identify each tag and, by association, each item associated on a one-for-one basis with such tags. (The corresponding document entitled EPC Radio-Frequency Identity Protocols Class-1 Generation-2 UHF RFID Protocol for Communications at 860 MHz-960 MHz Version 1.0.9 (often referred to as “EPC GEN2”) is hereby fully incorporated herein by this reference.)
At least some RFID-tag protocols permit an RFID tag to have any of a plurality of read states. The aforementioned EPC GEN2 approach, for example, provides for a so-called A inventory state, a B inventory state, and a selected flag (SL) state (pursuant to which an RFID tag is visible to all interrogation sessions). This permits, for example, a group of RFID tags to be inventoried without necessarily requiring each and every RFID tag to respond to the reader. A reader can be configured, for example, to request that RFID tags having an A inventory state respond to a read request while permitting RFID tags having a B inventory state to essentially ignore the read request.
Presently-proposed RFID tag-based systems that employ such approaches meet a wide variety of application requirements and needs. That said, the applicants have determined that not all potential needs are fully met by these presently-proposed approaches.
Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. Certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. The terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.